A number of techniques for creating a variety of patterns on the surface and inside of transparent substrates using pulsed laser radiation are well known.
One publication disclosing such techniques is the Russian invention #321422 to Agadjanov et. al., published on Nov. 16, 1970 (#140454529-33). The invention concerns a method of manufacturing decorative products inside a transparent material by changing the material structure by laser radiation. As disclosed, by moving a material relative to a focused laser beam, it is possible to create a drawing inside the material.
U.S. Pat. No. 4,092,518 to Merard discloses a method for decorating transparent plastic articles. This technique is carried out by directing a pulsed laser beam into the body of an article by successively focusing the laser beam in different regions within the body of the article. The pulse energy and duration is selected based upon the desired extent of the resulting decorative pattern. The effect of the laser is a number of three dimensional “macro-destruction” (fissures in the material of the article) appearing as fanned-out cracks. The pattern of the cracks produced in the article is controlled by changing the depth of the laser beam focus along the length of the article. Preferably, the article is in the form of a cylinder, and the cracks are shaped predominantly as saucer-like formations of different size arranged randomly around the focal point of the optical system guiding a laser beam. The device used to carry out this technique is preferably a multi-mode solid-state, free-running pulse laser used in conjunction with a convergent lens having a focal length from 100 to 200 mm.
U.S. Pat. No. 4,843,207 to Urbanek et al. discloses a method of creating controlled decorations on the surface of a hollow symmetrical transparent article. This technique is preferably carried out on glass. The glass is preconditioned with a coating on the outer surface of the glass being approximately 1.2 mm thick and made of a material having at least 75% absorption of laser radiation. The technique is also carried out using a laser having a wave of length of 0.5 to 2 microns acting upon the external coating through the wall of the cylindrical glass article. The laser beam moves so that it is focused on the surface of the cylinder, and moves about the axis of symmetry of the cylinder to irradiate the aforementioned surface coating. As a result, the irradiated portions of the surface coating go through a phase change and a pattern is formed.
U.S. Pat. No 5,206,496 to Clement et al. discloses a method and apparatus for providing in a transparent material, such as glass or plastic, a mark which is visible to the naked eye or which may be “seen” by optical instruments operating at an appropriate wavelength. The Clement et al. Patent describes a method and apparatus for producing a subsurface marking which is produced in a body such as bottle, by directing into the body a high energy density beam and bringing the beam to focus at a location spaced from the surface, so as to cause localized ionization of the material. In the preferred embodiment the apparatus includes a laser as the high energy density beam source. The laser may be a Nd-YAG laser that emits a pulsed beam of laser radiation with a wavelength of 1064 nm. The pulsed beam is incident upon a first mirror that directs the beam through a beam expander and a beam combiner to a second mirror. A second source of laser radiation in the form of a low power He—Ne laser emits a secondary beam of visible laser radiation with a wavelength of 638 m. The secondary beam impinges upon the beam combiner where it is reflected toward the second reflecting surface coincident with the pulsed beam of laser radiation from the Nd-YAG laser. The combined coincident beams are reflected at the reflecting surface via reflecting two other surfaces to a pair of movable mirrors for controlling movement of the beam. The beam then passes through a lens assembly into the body to be marked.
U.S. Pat. No. 5,575,936 to Goldfarb discloses a process and apparatus where a focused laser beam causes local destruction within a solid article, without affecting the surface thereof. The apparatus for etching an image within a solid article includes a laser focused to a focal point within the article. The position of the article with respect to the focal point is varied. Control means, coupled to the laser, and positioning means are provided for firing the laser so that a local disruption occurs within the article to form the image within the article.
U.S. Pat. No 5,637,244 to Erokhin discloses a technique which depends on a particular optical system including a diffraction limited Q-switched laser (preferably a solid-state single-mode TEM00) aimed into a defocusing lens having a variable focal length to control the light impinging on a subsequent focusing lens that refocuses the laser beam onto the transparent article being etched. The laser power level, operation of the defocusing lens, and the movement of the transparent article being etched are all controlled by a computer. The computer operates to reproduce a pre-programmed three-dimensional image inside the transparent article being etched. In the computer memory, the image is presented as arrays of picture elements on various parallel planes. The optical system is controlled to reproduce the stored arrays of picture elements inside the transparent material. A method for forming a predetermined half-tone image is disclosed. Accordance to the method, microdestructions of a first size are created to form a first portion of the image and microdestruction of a second size different from the first size are created to form a second portion of the image. Different sizes of microdestructions are created by changing the laser beam focusing sharpness and the radiation power thereof before each shot.
U.S. Pat. No. 5,886,318 to A. Vasiliev and B. Goldfarb discloses a method for laser-assisted image formation in transparent specimens which consists in establishing a laser beam having different angular divergence values in two mutually square planes. An angle between the plane with a maximum laser beam angular divergence and the surface of the image portion being formed is changed to suit the required contrast of an image.
U.S. Pat. No. 6,333,485 to Haight, et al. discloses method for minimizing sample damage during the ablation of material using a focused ultrashort pulsed beam. In one aspect the invention provides a method for laser induced breakdown of a material with a pulsed laser beam where the material is characterized by a relationship of flounce breakdown threshold versus laser beam pulse width that exhibits an abrupt, rapid, and distinct change or at least a clearly detectable and distinct change in slope at a predetermined laser pulse width value.
U.S. Pat. No. 5,656,186 to Mourou, et al. and Related U.S. Patent Documents RE 37,585 disclose method for laser induced breakdown of a material with a pulsed laser beam where the material is characterized by a relationship of fluence breakdown threshold versus laser beam pulse width that exhibits an abrupt and rapid.
U.S. Pat. No. 6,087,617 to Troitski et al. discloses a computer graphic system for producing an image inside optically transparent material. An image reproducible inside optically transparent material by the system is defined by potential etch points, in which the breakdowns required to create the image in the selected optically transparent material are possible. The potential etch points are generated based on the characteristics of the selected optically transparent material. If the number of the potential etch points exceeds a predetermined number, the system carries out an optimization routine that allows the number of the generated etch points to be reduced based on their size. To prevent the distortion of the reproduced image due to the refraction of the optically transparent material, the coordinates of the generated etch points are adjusted to correct their positions along a selected laser beam direction.
U.S. Pat. No. 6,333,486 to Troitski discloses a method for production of etch points inside transparent material, which have the same size but different brightness. Laser-induced damages produced by this method provide the reproduction of image gradation without changing of their spatial resolution.
U.S. Pat. No. 6,399,914 to Troitski discloses a method for producing laser-induced images inside the special transparent material containing special kinds of impurities, which decrease the damage threshold of the material that provides creation of small and without star structure laser-induced damages.
U.S. Pat. No. 6,417,485 to Troitski discloses a method and laser system for producing laser-induced damages inside transparent materials by controlling breakdown process development. At the beginning an applied laser radiation level just exceeds an energy threshold for creating a plasma condition inside the transparent material, and thereafter the energy level of the applied laser radiation is just maintain the plasma condition and is applied before the plasma condition extinguished, but after a shock wave associated therewith has passed.
U.S. Pat. No. 6,426,480 to Troitski discloses a method and system for producing single layer laser-induced damage portrait inside transparent material which are based on generation of small smoothed etch points of determined sizes and on control of their brightness without variation of their determined sizes.
U.S. Pat. No. 6,490,299 to Raevski et al. discloses method and laser system producing high quality laser-induced images inside transparent materials by using specific laser radiation generated by serial combination of both generation regims: a Q-switched mode and a free-running mode.
U.S. Pat. No. 6,509,548 to Troitski discloses a method and apparatus for producing high-resolution laser-induced damage images inside transparent materials by small etch points. The method is based on generation of the initial electron density in the relatively large volum, creation of the breakdown at a small part of the said volume and control of the energy amount enclosed inside the plasma.
U.S. Pat. No. 6,605,797 to Troitski discloses laser-computer graphics systems for producing images such as portraits and 3-D sculptures formed from laser light created etch points inside an optically transparent materials. The produced image has a high resolution like a computer graphic image from which it is derived, little fluctuation in gray shades, and has no discemable point structure.
U.S. Pat. No. 6,630,644 to Troitski et al. discloses a method for creating arrangement of damages for producing 3D laser-induced damage portraits with the space resolution, which is equal to the appropriate computer 3D model.
U.S. Pat. No. 6,664,501 to Troitski discloses a method for creating laser-induced color images within three-dimensional transparent material.
U.S. Pat. No. 6,670,576 to Troitski et al. discloses a method for producing laser-induced images inside transparent materials containing laser-induced color centers and laser-induced damages.
U.S. Pat. No. 6,720,521 to Troitski discloses a method for generating an area of laser-induced damage inside a transparent material by controlling a special structure of a laser radiation.
U.S. Pat. No. 6,720,523 to Troitski discloses a method for production of laser-induced images inside transparent material, when complete image information is lacking before production and is supplemented only during production.
U.S. Pat. No. 6,727,460 to Troitski discloses a system for high-speed production of high quality laser-induced damage images inside transparent materials. The system produces the said images by the combination of an electro-optical deflector and means for moving the article or focusing optical system.
U.S. Pat. No. 6,734,389 to Troitski discloses an apparatus for producing high quality laser-induced images inside optically transparent material by controlling breakdown process development and space structure of laser radiation.
U.S. Pat. No. 6,740,846 to Troitski et al. disclose a method for producing 3D laser-induced portrait by using several 2D regular portraits.
Analyzing the methods and apparatus disclosed in US Patents and other publications, we can make the following conclusion:                Two kinds of marks are used for production laser-induced images inside transparent materials: laser-induced damages appearing as a result of the breakdown and laser-induced etch points appearing as a result of photoionization. The last etch points is also named as color centers. These marks have different optical characteristics: the laser-induced damages scatter the light but color centers absorb the exterior light.        Laser-induced marks, which are used for creation of images on the surface, are created as result of the ablation of the material from its surface.        
This situation has the following disadvantages:                the use of different physical effects for creation of marks inside and on surface of transparent material demands to use different laser system for production of internal and surface marks;        the substantial removal of transparent material from its surface destroys the surface and make worse visibility of internal points of the image.        
The purpose of the present invention is the disclosure of a method and a system, which are able to produce laser-induced images containing both internal and surface points and which create the surface points under minimal (or without) surface transparent material removal.